A simple ¹H NMR based assay of total capsaicinoid levels in Capsicum using signal suppression in non-deuterated solvent

BACKGROUND: The heat of Capsicum fruits is routinely assayed using high-performance liquid chromatography (HPLC) to determine capsaicin (CA) and dihydrocapsaicin (DHC) levels. The assay can be time consuming, with each HPLC run typically lasting 10 min. Nuclear magnetic resonance (NMR) is eminently suitable for quantification of fruit extracts, although it has been largely ignored for quantitative chilli analysis. The present study describes a novel approach using solvent suppression in protic solvent (i.e. non-deuterated) to quantify total capsaicinoid levels in chilli extracts. RESULTS: Using solvent suppression techniques and maleic acid as an internal standard, capsaicinoid content in a series of accurately weighed standard samples was determined over a range between 40 and 720 ppm (0.13–2.35 mmolar) with high accuracy and precision. The measurement was linear over the entire range. This method was subsequently used with ten authentic Capsicum samples (seven chinense, two annuum and one baccatum) and showed an excellent correlation with the HPLC data. CONCLUSION: The results of the present study confirm that NMR in non-deuterated solvent can provide a rapid and robust assessment of the pungency of capsicum fruits.